Stereoselective palladium catalyzed cyclizations of enediyne compounds

Hydropalladium carboxylates, formed from pi-allylpalladium chloride dimer p lus carboxylic acids, have been shown to catalyze cyclization of structural ly diverse enediynes to form the corresponding six- or five-membered rings depending upon the reaction conditions. Some enediynes having an oxygen lin ker in an appropriate position under the similar condition yielded the corr esponding cyclopropanation products in highly stereoselective manner. A stu dy using deuterated formic acid has proven that the alkylpalladium intermed iates formed in our conditions were reduced by the pendant formate ligand. The dienediyne 10 yielded only the tricyclic product 12 in 67% yield, altho ugh it was expected to form the cyclic product 11. All these cyclizations s eemed to occur Yin the corresponding alkylpalladium intermediates I, which could proceed to the corresponding cyclic products depending on the reactio n conditions and the substrates. The study using deuterated formic acid cou ld provide an important information to understand the present cyclization m echanism. Overall the present study could play an important role in develop ing new synthetic methodologies for constructing complex polycyclic compoun ds.